External service interaction (DNS)
Summary: PortSwigger Research notes that inducing an application to interact with an arbitrary external service, such as a web or mail server, is not a vulnerability in itself and may even be intended behavior, though it can sometimes indicate a vulnerability with serious consequences. If DNS-based interactions can be triggered, interactions using other service types are normally possible too, and egress filters on the network layer may explain why a payload only produces a DNS lookup.
Bottom line: The ability to send requests to other systems can let the vulnerable server act as an attack proxy, reaching public third-party systems, internal systems in the same organization, or services on the application server's own loopback adapter - potentially exposing highly vulnerable internal services that external attackers cannot otherwise reach.
Read the original at PortSwigger Research ↗
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